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EP-2017-304

(Submitted on 08 Dec 2017)

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Abstract

We report measurements of charm-mixing parameters based on the
decay-time-dependent ratio of $D^0\to K^+\pi^-$ to $D^0\to K^-\pi^+$ rates. The
analysis uses a data sample of proton-proton collisions corresponding to an
integrated luminosity of $5.0$ fb$^{-1}$ recorded by the LHCb experiment from
2011 through 2016. Assuming charge-parity (CP) symmetry, the mixing parameters
are determined to be $x'^2=(3.9 \pm 2.7) \times10^{-5}$, $y'=(5.28 \pm 0.52)
\times 10^{-3}$, and $R_D=(3.454 \pm 0.031)\times10^{-3}$. Without this
assumption, the measurement is performed separately for $D^0$ and
$\overline{D}{}^0$ mesons, yielding a direct CP-violating asymmetry $A_D
=(-0.1\pm9.1)\times10^{-3}$, and magnitude of the ratio of mixing parameters
$1.00< |q/p| <1.35$ at the $68.3\%$ confidence level. All results include
statistical and systematic uncertainties and improve significantly upon
previous single-measurement determinations. No evidence for CP violation in
charm mixing is observed.

Efficiency-corrected ratios of WS-to-RS yields for (a) $ D ^{*+}$ decays, (b) $ D ^{*-}$ decays, and (c) their differences as functions of decay time in units of $ D ^0$ lifetime. Projections of fits allowing for (dashed line) no $ C\!P$ violation, (dotted line) no direct $ C\!P$ violation, and (solid line) direct and indirect $ C\!P$ violation are overlaid. The last two curves overlap. The abscissa of each data point corresponds to the average decay time over the bin. The error bars indicate the statistical uncertainties.

Tables and captions

Results of fits for different $ C\!P$ -violation hypotheses. The first contribution to the uncertainties is statistical and the second systematic. Correlations include both statistical and systematic contributions.

This ZIP file contains supplemetary material for the publication
LHCb-PAPER-2017-046. The files are:
Supplementary-LHCb-PAPER-2017-046.pdf : An overview of the extra figures
*.pdf, *.png, *.eps, *.C : The figures in various formats